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## `getSlotNumber`

### Signature

```solidity
function getSlotNumber() external view returns (uint64 slotNumber);
```

### Description

Gets the current `block.slotnum`.

Use this after `vm.rollSlot` to read the updated slot number. The Solidity compiler assumes `block.slotnum` is constant during a transaction and may optimize repeated reads away, especially with `--via-ir`. The cheatcode reads the current EVM value on every call.

Requires the Amsterdam EVM hardfork or later and reverts on earlier versions. Slot numbers are unsigned 64-bit values, as defined by [EIP-7843](https://eips.ethereum.org/EIPS/eip-7843).

### Returns

| Parameter | Type | Description |
|-----------|------|-------------|
| `slotNumber` | `uint64` | The current block slot number |

Solidity exposes `block.slotnum` starting with version 0.8.37.

### Examples

With `evm_version = "amsterdam"` configured:

```solidity [test/SlotNumber.t.sol]
function testSlotNumber() public {
    uint256 number = vm.getBlockNumber();
    uint256 timestamp = vm.getBlockTimestamp();

    vm.rollSlot(100);
    assertEq(vm.getSlotNumber(), 100);
    vm.rollSlot(101);
    assertEq(vm.getSlotNumber(), 101);

    assertEq(vm.getBlockNumber(), number);
    assertEq(vm.getBlockTimestamp(), timestamp);
}
```

### Related Cheatcodes

* [`rollSlot`](/reference/cheatcodes/roll-slot) - Sets the slot number
* [`getBlockNumber`](/reference/cheatcodes/get-block-number) - Gets the block number